The present invention relates to an automatic focus adjusting device having a plurality of focus detecting areas which is put to practical use as a single lens reflex camera or a video camera having an intelligent AF function capable of distinguishing an object in a scene to be photographed and automatically adjusting focus on the object.
In a conventional automatic focus adjusting device having a plurality of focus detecting areas, it has been proposed that object distance data are obtained relating to a plurality of focus detecting areas. The focus is adjusted on an object nearest to the photographer by driving the lens based on the rearmost, namely, the nearest object distance data, (see Japanese Laid-Open Patent Publication (Tokkaisho) No. 59-146028)
In an automatic focus adjusting device having a plurality of focus detecting areas, it is a problem how to determine the defocus amount for driving lens from the defocus amounts obtained relating to the plurality of focus detecting areas in order to focus on the main object to be photographed. In the Japanese Laid-Open Patent Publication No. 59-146028, the lens is driven based on the defocus amount of the rearmost or nearest object on the assumption that the object nearest to the photographer is the main object to be photographed. However, the object nearest to the photographer is not always the main object to be photographed. Therefore, disadvantageously, if the main object to be photographed is not the one nearest to the photographer, the main object cannot be focused.
On the other hand, in Japanese Laid-Open Patent Publication No. 61-279829, in a light measuring device for a camera in which light is measured by dividing an angle of view into a plurality of areas, it is proposed that the computing formula of the light measuring output is changed with the image magnification. However, this prior art relates to a light measuring device, and light measuring data and distance measuring data are of quite different character, and the ways of evaluating these data are also completely different. Consequently, this art has not proposed any suggestion to the solution of the technical problem of deciding defocus amount in an automatic focus adjusting device having a plurality of focus detecting areas.
In order to solve this technical problem, the inventors, have actually taken numerous sheets of photographs while changing a variety of photographing conditions such as the focal length of an objective lens, the a diaphragm aperture, the object distances and their distribution and the like, taking account of a variety of photographing circumstances, and statistically processed and examined the obtained data. As a result, the inventors have found that if the image magnification of an object in the scene, especially an object in the center of the scene is high, the object in the center of the scene is in many cases the main object to be photographed. On the contrary, if the image magnification thereof is low, the object nearest to the photographer is in many cases the main object to be photographed.
The present invention is based on such findings, and an object of the present invention is to provide an automatic focus adjusting device in which the focus is adjusted on the main object to be photographed at a high probability by selecting an argorithm for deciding a defocus amount for driving a lens out of defocus amounts relating to a plurality of areas of a scene in accordance with an image magnification.